This invention pertains to a novel process for the preparation of 3-methyltetrahydrofuran (MeTHF) from 3-(hydroxymethyl)tetrahydrofuran (HOMeTHF). More specifically, this invention pertains to a process for the conversion of HOMeTHF to MeTHF by contacting HOMeTHF with hydrogen in the presence of an acidic, supported catalyst comprising a Group VIII metal.
MeTHF has been produced in commercial quantities by the high pressure hydrogenation of citraconic anhydride and some of its derivatives according to the procedures disclosed in U.S. Pat. No. 5,536,854 and Published Japanese Patent Application (Kokai) 08-217,771. Since citraconic acid is formed from citric acid or, more economically, as a minor by-product, during maleic anhydride production, these routes to MeTHF are expensive and use a starting material which is not plentiful.
Processes for the production of MeTHF based on less expensive precursors and precursors independent of the production of other materials have been developed. Thus, U.S. Pat. No. 3,932,468, describes a process for isomerizing isoprene monoepoxide into 4-methyl-2,3-dihydrofuran using a nickel and hydrohalic acid catalyst. Although the hydrogenation of 4-methyl-2,3-dihydrofuran into MeTHF is relatively simple, the synthesis of the starting material, isoprene monoepoxide, is not. For example, the preparation of isoprene monoepoxide would require the use of classical (and expensive) epoxide manufacturing techniques such as the use of halohydrins or co-oxidation with aldehydes. Japanese Published Patent Application (Kokai) JP 08-291,158 describes another method for preparing MeTHF in which propylene is converted into 2-methylsuccinate esters by a double oxidative carbonylation in the presence of an alcohol. Although the reductive cyclization of the 2-methylsuccinate esters to MeTHF is facile, the double oxidative carbonylation reaction usually gives limited yields of the dicarbonylated products and requires expensive, reactive solvents to keep the reagents anhydrous.
Another method for the synthesis of MeTHF is disclosed in U.S. Pat. No. 3,859,369 and comprises the hydroformylation and reduction of 2-buten-1,4-diol into 2-methyl-1,4-butanediol which is converted to MeTHF by acid catalysis. U.S. Pat. Nos. 4,590,312 and 4,879,420 describe the conversion of 4-hydroxybutyraldehyde and its immediate precursor, 2-buten-1,4-diol, into MeTHF by reductive alkylation with formaldehyde followed by acid-catalyzed cyclization. In each case, the products were mixtures of MeTHF and tetrahydrofuran, which occurs in the hydroformylation process because isomerization accompanies the hydroformylation, limiting the yield of MeTHF by forming a tetrahydrofuran precursor. In the reductive alkylation processes, the intermediate products as well as the starting materials may form alcohols by hydrogenation. Only those hydrogenations occurring after an initial aldol condensation of the reactants with formaldehyde can form MeTHF. All other hydrogenations gave tetrahydrofuran or other byproducts.
The preparation of MeTHF also is disclosed in Published European Patent Application EP 0 727 422 and involves the hydrocyanation of methacrylate esters. A series of hydrolyses and esterifications form a diester which may be reductively cyclized to MeTHF using an acidic, copper chromite catalyst. In this case, not only were the starting materials expensive (although not as expensive as the citraconic anhydride derivatives), but also the synthesis required four steps. Japanese Published Patent Application (Kokai) JP 08-217,708 describes a process for producing MeTHF by the hydroformylation of methacrylate esters to form mixtures of the xcex1-formylisobutyrate and the xcex2-formylisobutyrate esters using synthesis gas. Japanese Published Patent Application (Kokai) JP 08-217,770 discloses a similar hydroformylation using methyl formate as the C-1 source. In both of these hydroformylation processes, hydrogenation of the resulting xcex2-formylisobutyrate ester over a copper chromite catalyst produced MeTHF. One further hydroformylation route reported in Published European Patent Application Publication EP 747,373 consists of (1) the hydroformylation of isobutenyl alcohol (2-methyl-2-propen-1-ol) to form 4-hydroxy-3-methylbutyraldehyde which (2) was readily hydrogenated with nickel catalysts to 2-methyl-1,4-butanediol and which (3) was cyclized to MeTHF by acid catalysis.
Japanese Published Patent Application (Kokai) JP 2001-226366 (Kuraray Co. Ltd.) discloses dehydrating 3-hydroxy-3-methyltetrahydrofuran in the presence of an acidic substance to produce 3-methyldihydrofuran which may be hydrogenated to 3-methyltetrahydrofuran. Japanese Published Patent Applications (Kokai) JP 2001-039965 and JP 2001-163866 (Kuraray Co. Ltd.) disclose the preparation of 3-hydroxy-3-methyltetrahydrofuran by oxidizing 3-methyl-3-buten-ol with hydrogen peroxide in the presence of a zeolite. This method has limitations for commercial use since it requires relatively expensive and potentially explosive hydrogen peroxide.
U.S. Pat. No. 5,856,527 discloses a process for the preparation of 3-alkyltetrahydrofurans by a two-step process, wherein 2,3-dihydrofuran is reacted with an acetal to form an intermediate compound, which may be converted to a 3-alkyltetrahydrofuran by contacting the intermediate with hydrogen in the presence of a catalytic amount of a Group VIII noble metal or rhenium and a strong acid catalyst. U.S. Pat. No. 5,856,531 discloses a two-step process wherein (1) 2,3-dihydrofuran is reacted with a trialkyl orthoformate in the presence of an acidic catalyst to produce 2-alkoxy-3-dialkoxymethyl)-tetrahydrofuran, and (2) the intermediate is contacted with hydrogen in the presence of a catalyst system comprising a Group VIII noble metal or rhenium and a strong acid to convert the intermediate to a mixture of MeTHF and HOMeTHF.
U.S. Pat. No. 5,912,364 discloses the preparation of MeTHF by contacting 3-formyltetrahydrofuran (3-FTHF) with hydrogen in the presence of a catalyst system comprising a Group VIII noble metal or rhenium and a strong acid under hydrogenolysis conditions of temperature and pressure. The disclosed process typically produces a mixture of MeTHF and HOMeTHF. This patent also discloses processes for the preparation of 3-FTHF by contacting 2,5-dihydrofuran with synthesis gas comprising carbon monoxide and hydrogen in the presence of a rhodium-phosphorus catalyst system according to known hydroformylation procedures. U.S. Pat. No. 5,945,549 discloses a process for the recovery of an aqueous solution of 2- and 3-formyltetrahydrofurans (FTHF""s) produced by the rhodium-catalyzed hydroformylation of 2,5-dihydrofuran wherein the FTHF""s are recovered as an equilibrium mixture of 2- and 3-FTHF and their hydrates (2- and 3-[di(hydroxy)methyl]tetrahydrofuran) from a hydroformylation product solution comprising a rhodium catalyst, 2- and 3-FTHF and an organic hydroformylation solvent. These known methods for the production of MeTHF starting with 3-FTHF suffer from one or more disadvantages such as low reaction yields, the co-production of other compounds, which have limited utility and/or the use of corrosive acids.
A process has been developed for the conversion of HOMeTHF to MeTHF by contacting HOMeTHF with hydrogen in the presence of certain acidic, supported catalysts. In its broader aspects, the present invention provides a process for the preparation of MeTHF which comprises contacting HOMeTHF with hydrogen in the presence of an acidic, supported catalyst comprising a Group VIII metal such as nickel, cobalt, platinum, palladium, and the like on a catalyst support material under hydrogenation conditions of temperature and pressure.
The MeTHF produced in accordance with the present invention is useful as an industrial solvent and, more importantly, as a monomer in the manufacture of polymers such as elastomers. MeTHF is used extensively as a co-monomer for elastomers giving modified glass transition temperatures and broader elastic ranges.
The process of the present invention provides a means for the preparation of MeTHF by contacting HOMeTHF with hydrogen gas in the presence of a catalytically-effective amount of an acidic, supported catalyst comprising (i) a Group VIII metal and (ii) an acidic catalyst support material. The hydrogenation process may be carried out at a total pressure of about 1 to 690 bars gauge (barg; about 15 to 10,012 pounds per square inchxe2x80x94psig), more typically at a pressure of 10 to 68 barg, and preferably at a pressure of 13 to 55 barg. The temperature at which the process is carried out may be in the range of about 200 to 500xc2x0 C., preferably about 260 to 350xc2x0 C. The reaction time required to give satisfactory results will vary significantly depending upon a number of process variables such as process temperature and pressure and the particular catalyst employed. The process preferably is operated in a manner that conversion of the HOMeTHF reactant is maintained below 85 mole percent to maximize conversion to MeTHF product and minimize conversion to by-products.
The process of the present invention normally is carried out in the liquid phase in the presence of an extraneous solvent, typically an inert solvent, i.e., a solvent, which is non-reactive under the process conditions. Water is a convenient solvent when 3-formyl THF (3-FTHF), from which the HOMeTHF starting material may be derived, is recovered from a hydroformylation process according to the process described in U.S. Pat. No. 5,945,549. However, polar solvents compatible with water and the high reaction temperatures may be used. Examples of such polar solvents include tetrahydrofuran, tetrahydropyran, alkanols such as isopropanol, ethanol, methanol, and butanol, and the ethylene glycol ethers such as 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, and 2,5,8,11-tetraoxadodecane. The amount of solvent used may vary from about 1 to 99 parts by weight per part by weight of the HOMeTHF reactant. More common amounts of solvent although not necessarily preferred are 10 to 90 parts by weight solvent per part by weight of the HOMeTHF reactant with 20 to 80 parts solvent (same basis) being most common.
The catalysts useful in the process of the present invention are acidic, supported catalysts comprising a Group VIII metal, e.g., nickel, cobalt, platinum, palladium, and the like, on an acidic catalyst support material. Examples of the support material include alumina, zirconia, silica, titania, vanadium oxide, molybdenum oxide, and mixed metal oxides comprising any combination of zirconium, aluminum, titanium, cerium, calcium, silicon, magnesium, copper, barium, chromium, manganese, vanadium, iron, and strontium such as zirconium-titanium and molybdenum-zirconium mixed oxides. The support material also may be selected from salts having low solubility in water and organic solvents such as, for example, the phosphate, monohydrogen phosphate, dihydrogen phosphate, sulfate, monohydrogen sulfate titanate, zirconate, chromate, vanadate, aluminate, and silicate salts of aluminum, zirconium, titanium, neodymium, niobium, molybdenum, cerium, and other rare earth metals. The preferred support materials are zirconium oxide, aluminum oxide, and zirconium phosphate. The amount of Group VIII metal which may be present on the support material may vary from about 0.001 to 50 weight percent, more typically about 1 to 20 weight percent, based on the total weight of the catalyst. The amount of Group VIII depends, in part, upon the particular metal used. For example, a supported nickel catalyst may contain up to about 60 weight percent nickel, e.g., from about 1 to 60 weight percent nickel, whereas a supported palladium catalyst typically contains less metal, e.g., up to about 0.1 to 5 weight percent palladium. The preferred acidic, supported catalysts comprise about 1 to 15 weight percent nickel on a catalyst support material selected from aluminum oxide, zirconium oxide, molybdenum oxide, and zirconium phosphate.
The supported catalysts useful in the present invention comprise acidic catalysts. The acidity of the solid acidic catalysts can be measured and characterized according to known techniques and procedures, for example, Temperature-Programmed Desorption (TPD) using ammonia, monomethylamine or pyridine. See, for example, Tanabe, et al., New Solid Acids and Bases and their Catalytic Properties, Vol. 51, Elsevier Science Publishing Company, Inc., New York (1989). By xe2x80x9cacidic catalystsxe2x80x9d we mean catalysts which have acid site densities of greater than about 6xc3x97105, preferably greater than about 1xc3x97106, acid sites per square meter as measured by TPD using monomethylamine. The catalyst support material may be alumina, titania, zirconia, molybdenum oxide, vanadium oxide or a mixed oxide which can be rendered more acidic by the addition of a Brxc3x8nsted acid to the unmodified catalyst support material. Examples of Brxc3x8nsted acids which may be used include inorganic acids such as sulfuric, phosphoric and hydrohalic acids, e.g., hydrogen chloride, hydrogen bromide and hydrogen iodide. The Brxc3x8nsted acid also may be an organic acid such as carboxylic acids, e.g., acetic acid, or a sulfonic acid, e.g., an alkyl- or aryl-sulfonic acid. Acidification of the catalyst may occur prior to and/or after the deposition of the Group VIII metal. Alternatively, the acidic catalysts employed in the present invention may comprise a support material containing an inherently acidic oxide such as the oxides of niobium, neodymium, molybdenum, tungsten, silicon and boron. The presence of one or more oxides of Group VB-VIIB is known to increase the acidity of Group III and Group IV metal oxides such as alumina, zirconia, ceria, and the like. See, for example, Makoto Hino and Kazushi Arata, Bull. Chem. Soc. Jpn., 67, 1472-1474, (1994); J. G. Santiesteban, J. C. Vartuli, S. Han, R. D. Bastian, and C. D. Chang, Journal of Catalysis, 168, 431-441 (1997); and E. Lopez-Salinas, J. G. Hernandez-Cortez, I. Schifter, E. Torres-Garcis, J. Navarrete, A. Gutierrez-Carrillo, T. Lopez, P. P. Lottici, D. Bersani, Applied Catalysis A: General 193, 215-225, (2000). The catalyst support material also may comprise a hetero-poly-acid having Keggin type structure and based on silica, tungsten, molybdenum and/or phosphorus. Specific examples of such acidic oxides and hetero-poly-acids include zirconia with molybdenum oxide, zirconia with tungsten oxide, silicotungstic acid H4O40SiW12, phosphotungstic acid hydrate H3O40PW12, 12-molybdophosphoric acid H3MoO7P, 12-tungstophosphate H3O7PW, and the like.
The acidic catalysts, which may be employed advantageously in the hydrogenation process of the present invention include certain catalysts which are commercially available such as Criterion Catalyst 424 (C-424) comprising 3.0-4.5 weight percent nickel on alumina modified with phosphorus (6.0-9.0%) and molybdenum (16.5-22.5%) oxides. Alternatively, useful acidic catalysts may be prepared using procedures known to those skilled in the art.
The catalytic hydrogenation process of the present invention is carried out without co-feeding a strong acid, iodine or iodine compound according to the process described in U.S. Pat. No. 5,912,364.
Prior to their use, the catalysts comprising one or more catalytically-active Group VIII metals deposited on a catalyst support material are reduced with hydrogen to convert the metal salts into zero valent active metal catalyst. This pre-reduction generally takes place at temperatures between 200xc2x0 C. and the calcining temperature with 250 to 500xc2x0 C. being more preferred and 300 to 400xc2x0 C. most preferred.
The process provided by the present invention provides a means for the production of MeTHF from HOMeTHF. The HOMeTHF may be obtained by contacting FTHF with hydrogen gas in the presence of a catalytically-effective amount of a hydrogenation catalyst comprising a Group VIII metal and under hydrogenation conditions of pressure and temperature which converts the FTHF to HOMeTHF. Thus, a second embodiment of our invention concerns a process for the preparation 3-methyltetrahydofuran (MeTHF) by the steps comprising:
(1) contacting 3-formyltetrahydrofuran (FTHF) with hydrogen in the presence of a hydrogenation catalyst comprising a Group VIII metal under hydrogenation conditions of pressure and temperature to convert the FTHF to 3-(hydroxymethyl)tetrahydrofuran (HOMeTHF); and
(2) contacting the HOMeTHF produced in step (1) with hydrogen in the presence of an acidic, supported catalyst comprising (i) a Group VIII metal and (ii) an acidic catalyst support material under hydrogenation conditions of temperature and pressure to convert HOMeTHF to MeTHF.
The catalyst utilized in step (1) preferably is a supported nickel catalyst containing up to about 60 weight percent nickel, e.g., from about 1 to 60 weight percent nickel, based on the total weight of the catalyst. The preferred step (1) supported catalysts comprise about 1 to 15 weight percent nickel on a catalyst support material. Steps (1) and (2) of the second embodiment of the present invention may utilize the same catalyst, i.e., an acidic, supported catalyst comprising (i) a Group VIII metal and (ii) an acidic catalyst support material, wherein milder conditions of temperature and/or pressure are employed in step (1) to produce HOMeTHF, or primarily HOMeTHF. Step (1) of the second embodiment, like the second step, normally is carried out in the liquid phase in the presence of an extraneous solvent, typically an inert solvent, i.e., a solvent, which is non-reactive under the process conditions. Water is a convenient solvent when 3-FTHF is recovered from a hydroformylation process. However, polar solvents, such as those described above, which are compatible with water and the high reaction temperatures also may be used in the first step.